Electric circuit breaker



April 2, 1963 Filed 061.. 12, 1960 K. w. KLEIN ETAL 3,084,236

ELECTRIC CIRCUIT BREAKER 2 Sheets-Sheet l Inventors: Keith W.'K|ein, David. B. Powell,

Attorney.

April 2, 1963 K. w. KLEIN ETAL ELECTRIC CIRCUIT BREAKER 2 Sheets-Sheet 2 Filed 001;. 12, 1960 Inventors: Keith W. Klein,

David B.Fowell,

Atto'r n e5.

United States Patent i 3,ti84,236 ELECTRIC CIRQUHT BREAKER Keith Wiiham Kiein, Simshury, and David Barton Poweli, Bnistoi, Conn assignors to General Electric Company, a corporation of New York Filed Oct. 12, 1%0, Ser. No. 62,184 19 Claims. (Cl. zoo-nos Our invention relates to electric circuit breakers and particularly to electric circuit breakers having adjustable current responsive tripping means.

Electric circuit breakers of the molded-case type commonly include current responsive means which are adustable by the user through a predetermined range of adustment by means accessible externally of the molded casing of the circuit breaker. In order to facilitate manufacture of such circuit breakers, and also to provide greater accuracy of operation, means has also been provided for ad ustably pre-setting the permitted range of user adjustment. The pre-setting adjustment is preferably accomphshed at the factory, and then sealed to prevent further change. In a particular construction, the pre-settable means includes means for adjusting each end point of the permitted user adjustment range independently of the other end point, thereby permitting variation of the extent of the range of user adjustment as well as its end points. Such a construction is shown, for example, and claimed in its broader aspects, in copending application Serial No. 56,302, Hobson and Murphy, filed September 15, 1960, 21nd assigned to the same assignee as the present invenion.

It is an object of the present invention to provide an electric circuit breaker including adjustable current responsive means of the type described which is simpler and less expensive than that of prior devices.

It is another object of the invention to provide an electric circuit breaker including current responsive tripping means contained in an enclosure and having a control device accessible for operation from outside the enclosure and movable between predetermined limits and means also accessible from outside the enclosure for varying the range of adjustment of the trip device brought about by moving the control device between the aforesaid limits.

In accordance with the invention, we provide an electric circuit breaker having cur-rent responsive means including a rotatable cam member accessible for operation from outside of the circuit breaker. The cam member acts on a cam (follower member which, in turn, is connected to a sensitivity-controlling member, moving it through a predetermined range of movement as determined by the cam.

-For the purpose of predetermining the extent of the range of adjustment brought about by the cam member, the cam member itself is made bodily adjustable in its position with respect to the pivot of the cam follower member. This variation is accomplished, moreover, without affecting the position of the cam follower member corresponding to a predetermined initial rotational setting of the cam member, by causing the bodily movement of the cam member to be along a path which is parallel to the surface of the cam follower member at the predetermined setting. Separate means is also provided for adjustably varying the sensitivity of the device at the aforesaid predetermined setting of the cam member.

In accordance with the invention in one form, we provide an electric circuit breaker having current responsive means of the magnetic type including a magnetic field piece and an armature biased away from the field piece. A pivoted cam follower member acts as a stop for limiting movement of the armature away from the field piece. The cam follower member has a cam surface engag by Patented Apr. 2, 1963 ice rotatable cam. The cam is also bodily movable toward or away from the pivot of the cam-follower member, along a path which is parallel to the cam surface of the cam follower member at a predetermined setting of the cam. Bodily movement of the cam therefore does not alter the position of the armature at this setting, but does alter the amount of movement of the cam follower caused by the cam at all other settings. For the purpose of permitting adjustment of the sensitivity of the device at the predetermined setting, however, means is provided for adjusting the tension of armature-biasing spring.

The invention will be more fully understood from the following detailed description, and its scope will be pointed out in the appended claims.

In the drawings,

'FIGURE 1 is a side elevation View of a circuit breaker incorporating the invention, a portion of the outer casing being broken away;

FIGURE 2 is a partial topplan view of the circuit breaker of FIGURE 1, a portion of the cover being broken away;

FIGURE 3 is a perspective view of the separately enclosed trip unit of the circuit breaker of FIGURE 1;

FIGURE 4 is a section view of the trip unit of FIG- URE 3, taken on the plane indicated by the line l-dof FIGURE 3;

FIGURE 5 is an exploded perspective view of a portion of the adjusting mechanism of the trip unit of FIGURE 3, and

FIGURE 6 is a plan view of a portion of the adjusting mechanism of the trip unit of FIGURE 3.

The invention is shown in the drawings as embodied in a multi-pole electric circuit breaker comprising a main insulating casing having a base 10 and a cover 11. The base 10 includes three elongated side-by-side pole chambers, not shown, each containing a pair of relatively separable contacts 9, at one end, for interrupting the electric circuit through the respective poles. Operating mechanism, not shown, is also provided for opera-ting the contacts in unison between open and closed circuit positions. The operating mechanism may be of any suitable form, such for example as shown in Patent No. 2,921,169 assigned to the same designee as the present invention, and includes a manually engageable handle 12. The circuit breaker also includes a releasable member 8, which is normally restrained but which is releasable to cause automatic opening of the contacts 9.

For the purpose of restraining the releasable member 8 and releasing it upon the occurrence of predetermined current conditions, current responsive means is provided comprising a trip unit indicated generally at 13. The trip unit 13 includes a generally rectangular insulating enclosure or housing 14, having an incoming conductor .15 and an outgoing conductor 16 interconnected by a U-shaped intermediate conductor 17, for each of the pole chambers. The conductors 15, 16 and 17 are relatively rigid, and are interconnected by suitable means such as by welding or brazing. The trip unit as a whole is supported in the main base 10 by having the incoming and outgoing conductors 15 and 16 respectively, rigidly mounted to the base 10 by suitable means, not shown.

The trip unit v13 further includes a trip bar 19 of insulating material, which is pivotally supported on a fixed pivot pin 20 by means of a supporting bracket 19A which includes a recess or aperture providing a latch surface 21 for releasably restraining the end of the releasable member 8. The trip bar 1) extends transversely across all three pole chambers, and is adapted to be acted upon by the current responsive means associated with each pole chamber in a manner to be described. A biasing spring, not shown, is provided, biasing the trip bar 19 and the member 19A toward latched position, i.e., counterclockwise as shown.

7 For the purpose of actuating the trip bar 19 to cause release of the member 8 upon the occurrence of electrical overload conditions in any of the pole chambers, current responsive means is provided in each of the pole chambers. The current responsive means includes a stationary magnetic core or field piece 22, which straddles one leg of the U-shaped conductor portion '17 and is retained in position by means of the screw 18. The screw 18 preferably extends through aligned clearance holes in the wall of the housing 14, the portion of conductor 17 adjacentthereto, and the field piece itself, and threads into the opposite leg of the U-shaped conductor 17. The field piece 22, moreover, perferably abuts directly against raised abutments not shown, on the housing wall to provide clearance for the conductor 17 between it and the housing Wall. This permits flexing movement of the conductor 15, facilitating mounting and connecting ofthe as sembly and minimizing danger of breakage of the housing by such mounting. V

The core or field piece 22 is generally U-shaped forming pole portions 23. An armature assembly is mounted adjacent each of the field pieces 22 and comprises an armature portion 24, an elongated cam-follower portion 25 and a trip bar actuating portion 26. The main body portion of the armature assembly is U-shaped so that the cam follower portion 25 comprises the bight portion of the assembly and the armature portion 24 is an extension of the bight portion. The trip bar actuating portion 26 comprises a portion of one of the opposed sides of the armature assembly.

In operation, the existence of excessively high current in the conductors .15, 16 and 17 creates a magnetic field appearing at the pole portions 23 of the field piece 22, This field attracts the armature 24, causing it to rotate about its pivotal support 20, bringing the projection 26 into engagement with the trip bar 19, rotating it clock wise to cause release of the member 8.

The armature assembly is biased to its unattracted position by means of a bias spring 27 which engages the armature assembly'at one end and has its other end carried by an adjustable supporting lever 28. The lever 28 comprises a relatively thin fiat strip of metal, extending through an aperture 29 in the casing of the trip unit and retained in position by a screw 30 threadedly engaged in the insulating material of the casing. The marginal portions of the aperture 29 are shaped to provide knife-edge pivot supports for the member 28, whereby adjustment of the screw 30 rocks the member 28 about the knife-edge portions to adjust the tension of the spring 27, thereby varying the sensitivity of the magnetic current responsive means.

The sensitivity of the magnetic current responsive mechanism may also be adjusted, in accordance With the invention, by varying the position of the armature 24. For this purpose, there is provided a generally disc-like cam member 32, fixedly supported on a supporting shaft 33 which carries a threaded insulating adjusting nut 34 at one end, accessible for operation from outside of the main circuit breaker housing.

The shaft 133 is supported at its inner end in a bearing aperture in the trip unit housing. The assembly comprising the shaft 33, the cam 32, and the nut 64 is normally rotatable as a unit, causing the cam 32- to act on the cam follower surface 25 of the armature assembly, to thereby vary the normal or unattracted position of the armature portion 24 between maximum and minimum gap positions. Thus when the cam 32 is turned to a position which permits the cam follower portion 25 of the armature assembly to approach closer to the shaft 33, the armature 24 is relatively farther away from the field piece 22. Likewise, when the shaft 32 is turned to a position in which the cam follower surface at 25' is relatively farther away from the shaft 33, the armature portion 24 is moved relatively 4 closer to the field piece at 22. It will be observed that this permits the user to vary the setting of the armature through a predetermined range of adjustment by rotating the nut 34, but not outside of that range.

The cam member 32 is fixedly attached to the shaft 33 and the shaft 33 is threadedly engaged in the adjusting nut 34. The axial position of the cam 32 with respect to the nut 34, and therefore its distance from the pivot 29 of the armature assembly, may be varied by inserting a screwdriver in the slot 36 of the shaft 33 to restrain the shaft 33 and its cam member 32 from rotation, and simultaneously turning the adjusting nut 3 causing the shaft 33 to thread axially through the nut 34. For this purpose, the nut 34 is provided with notches 34A to facilitate turning. This moves the cam 32 bodily along the line of the axis of the shaft '33 toward or away from the pivot 20. The cam 32 may therefore be caused to engage the cam follower portion at points of differing distances from the pivot 20, thereby varying the mechanical advantage of the cam action on the armature assembly. The slot 36 is preferably made non-symrnetrical, as shown, and bears a predetermined directional relation to the cam, as a means of indicating the position of the cam.

It is an important aspect of the invention, that at one setting of the cam member (i.e., the maximum gap position in the form shown), the cam follower surface 25 is parallel to the axis of the shaft 33. Thus the bodily shifting of the cam does not affect the position of the cam follower assembly corresponding to this setting of the cam. The lower limit of gap-closing caused by the cam may therefore be adjusted without disturbing the maximum setting.

Calibration pr0cedure.The steps in calibrating or adjusting the trip device are as follows. Cam 32 is turned to the position which provides the largest air gap (maximum position), and the tension of the spring, 27 is adjusted by rotating the screw 30, until the armature closes at the desired level of current.

The cam 32 is then turned to the position which provides the minimum air-gap (minimum position), and again the current level is checked to determine that required to cause actuation. If this current level is found to be too high, it indicates that the air gap provided at this setting is too large and must be reduced. The air gap is reduced by holding the cam from rotating by inserting a screwdriver in the slot 36 of the outer end of the shaft 33, and rotating the nut 34 in a directionto cause the shaft and cam 32 to move axially downward as shown, i.e., closer to the pivot 20 of the armature assembly. This forces the armature assembly slightly further clockwise, as shown, reducing the air gap.

If the current level required to trip is found to be too low at the minimum setting, the shaft 33 and the cam 32 are held from rotation in the manner described above and the nut '34 is turned in a direction to cause the cam and shaft to move axially upwardly and away from the pivot 20, thereby permitting the spring 27 to move the armature assembly slightly counterclockwise, thereby increasing the air gap.

As previously noted, at the maximum position of the cam, the cam follower surface 25 is parallel to the shaft 33. Because of this, movement of the cam axially up or down does not affect the maximum position of the armature assembly. Thus the current value required to cause actuation of the device when the knob 34 is at the maximum setting is not altered or affected by the subsequent axial adjustment of the cam to vary the current required to cause actuation when the knob 34 is at the: minimum setting.

Once the calibration or factory adjustment described above has been accomplished, a cap member 38 is pushed onto the adjusting nut 34, a projecting portion 39 entering the recess 40 of the nut 34. The cap 38 prevents access to the slot 36 and also provides a stop 41 cooperating with a projection 42 extending inwardly from the margin of the aperture 43 on the cover 11, to limit rotation of the knob assembly to slightly les than 360-".

It will be understood that the trip unit 13 may, of course, also include other current responsive means in addition to the magnetic apparatus described. Thus, for example, a bimetallic strip, not shown, may be provided for each pole, disposed to be heated by current in the conductors 17, and arranged to act upon the trip bar 19 to provide thermal tripping.

While we have described a particular embodiment of our invention, it will be readily apparent that many modiiications thereof may be made, and we therefore intend, by the appended claims, to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric control device including a member movable to vary the sensitivity of said device, means for adjustably positioning said movable member comprising a pivoted member having a cam follower portion, a cam member acting on said cam follower portion, and means for bodily moving said cam member to a plurality of different positions to act on said cam follower portion at corresponding differing distances from the pivotal support of said pivoted member selectively, said cam member being rotatable about a predetermined axis of rotation when in each of said positions to move said cam follower portion in a direction substantially perpendicular to said axis of rotation.

2. An electric control device comprising a member movable to vary the sensitivity of said device, means for adjustably positioning said movable member comprising a member having a pivotal support and a cam follower surface, a rotatable cam member acting on said cam follower surface, means for bodily moving said cam member to a plurality of different positions to act on said cam follower surface at corresponding differing distances from said pivotal support selectively, said cam member being rotatable about a predetermined axis of rotation when in each of said positions to move said cam follower portion in a direction substantially perpendicular to said axis of rotation said cam member being movable by said positioning means along a path extending parallel to said cam follower surface.

3. A magnetic current responsive device comprising a conductor, a magnetic field piece disposed to be energized by current through said conductor, an armature supported for movement toward and away from said field piece,

means limiting movement of said armature away from said field piece comprising a cam follower member supported upon a pivotal support, means connecting said cam follower member with said armature, said cam follower member having an elongated cam follower surface, -a rotatable cam member having a portion in engagement with the said cam follower surface, said cam member being bodily movable to a plurality of different positions to engage said cam follower surface at points located at corresponding differing distances from said pivotal support selectively, whereby to vary the mechanical advantage of said cam member on said cam follower member.

4. The magnetic current responsive device comprising a conductor, a magnetic field piece disposed to be energized by current through said conductor, an armature supported for movement toward and away from said field piece, means limiting movement of said armature away from said field piece comprising a cam follower member supported upon a pivotal support, means connecting said cam follower member with said armature, said cam follower member having an elongated cam follower surface, a rotatable cam member having a portion in engagement with said cam follower surface, said cam member being adjustably movable to engage said cam follower surface at points located at differing distances from said pivotal support selectively, whereby to vary the mechanical advantage of said cam member on said cam follower memher, the path of adjustable movement of said cam member extending substantially parallel to said cam follower surface in at least one possible position of said cam follower member.

5. A magnetic current responsive device comprising an enclosure, a conductor mounted in said enclosure, a magnetic field piece supported in said enclosure and arranged to be energized by current through said conductor, an armature supported in said enclosure for movement toward and away from said field piece, spring means acting on said armature and biasing said armature away from said field piece, means accessible externally of said enclosure for adjusting the tension of said spring means, means limiting movement of said armature away from said field piece comprising a cam follower member pivotally supported in said enclosure and having an elongated cam follower surface, a rotatable cam member supported in said enclosure and having a cam portion engaging said cam follower surface, means accessible externally of said enclosure for rotating said cam member, and means for adjustably positioning said cam member to engage said cam follower surface at points of diifering distance from the pivotal support of said pivoted member.

6. A trip unit for an electric circuit breaker comprising an insulating housing, an electrical conductor supported in said insulating housing, a magnetic field piece supported in said insulating housing and arranged to be energized by current through said conductor, an armature supported in said insulating housing for movement toward and away from said field piece, a biasing spring acting on said armature and biasing said armature for movement away from said magnetic field piece, a cam follower member pivotally supported in said insulating housing and having an elongated cam follower surface, means connecting said cam follower member to said armature to limit the movement of said armature away from said magnetic field piece in accordance with the position of said cam follower member, a cam member rotatably supported in said insulating housing, means accessible externally of said insulating housing for rotating said cam member, and means accessible externally of said housing for adjustably positioning said cam member to act on said cam follower member at points of differing distance from said pivotal support of said cam follower member selectively.

7. An electric circuit breaker comprising an insulating housing, at least one pair of separable contacts mounted in said housing, manually operable'operating mechanism mounted in said insulating housing and including a manually eng-ageable operating hand, a releasable member releasable to cause automatic opening of said contacts, means for causing release of said releasable member upon the occurrence of predetermined electrical conditions comprising a current responsive device having a portion movable to vary the sensitivity thereof, a cam follower member having a pivotal support in said insulating housing, means connecting said cam follower member to said movable portion of said current responsive device, a cam member rotatably supported in said housing and engaging said cam follower member, position adjusting means for adjustably positioning said cam member to engage said cam follower member at points of differing distance from said pivotal support of said cam follower member, said cam member being movable along a path of movement extending substantially parallel to said cam surface in at least one possible position of said cam follower member, means for preventing access to said cam position adjusting means when said current responsive device is in said housing, and means accessible externally of said housing for rotating said cam member.

8. A multi-pole electric circuit breaker comprising a main insulating housing having at least two pole chambers, at least one pair of relatively movable contacts in each of said pole chambers, operating mechanism contamed in said insulating housing and including a manually operable handle, a releasable member releasable to cause automatic opening of said relatively movable contacts, current responsive means for causing release of said releasable member upon the occurrence of predetermined current conditions through said contacts comprising a common trip bar extending across all of said pole chambers, a restraining latch normally engaging and restraining said releasable member, means connecting said common trip bar and said restraining latch to cause releasing movement of said restraining latch upon predetermined movement of said common trip bar, a current responsive device connected in circuit with each of said pairs of relatively movable contacts respectively, means connecting each of said current responsive means to said common trip bar, means for adjusting the current level at which each of said current responsive devices operates to cause releasing movement of said trip bar comprising a cam follower member pivotally supported in said insulating housing, means operated by said cam follower member for modifying the current sensitivity of at least one of said current responsive devices, a rotatable cam member engaging said cam surface of said cam follower member, means for adjustably positioning said cam member to engage said cam surface at points of differing distances from the pivotal support of said cam follower member whereby to vary the mechanical advantage of said cam member on said cam follower, said cam member being adjustably positionable along a path of movement extending substantially parallel to said cam surface in at least one possible adjusted position of said cam follower member, and means accessible from outside of said main housing for rotating said cam member.

9. A multi-pole electric circuit breaker comprising a main insulating housing having at least two pole chambers, at least one pair of relatively movable contacts in each of said pole chambers, operating mechanism contained in said insulating housing and including a manually operable handle, a releasable member releasable to cause automatic opening of said relatively movable contacts, current responsive means for causing release of said releasable member upon the occurrence of predetermined current conditions through said contacts comprising a separately enclosed trip unit removably mounted in said main insulating housing and including a common trip bar extending across all of said pole chambers, a restraining latch carried by said trip unit normally and engaging and restraining said releasable member, means connecting said common trip bar and said restraining latch to cause the releasing movement of said restraining latch upon predetermined movement of said common trip bar, a current responsive device mounted in said trip unit and connected in circuit with each of said pairs of relatively movable contacts respectively, means connecting each of said current responsive means to said common trip bar, means for adjusting the current level at which each of which said current responsive devices operates to cause releasing movement of said trip bar comprising a cam follower member pivotally supported in said trip unit housing, means operated by said cam follower member for modifying the current sensitivity of at least one of said current responsive devices, a rotatable cam member supported in said trip unit housing engaging said cam surface of said cam follower member, means for adjustably positioning said cam member to engage said cam surface at points of difiering distances from the pivotal support of said cam follower member whereby to vary the mechanical advantage of said cam member on said cam follower, said cam member being adjustably positionable on a path of movement extending substantially parallel to said cam surface in at least one possible adjusted position of said cam follower member, said cam positioning means being carried by said trip unit housing and accessible for operation from outside of said main housing.

10. A multi-pole electric circuit breaker comprising a main insulating housing having at least two pole chambers, at least one pair of relatively movable contacts in each of said pole chambers, operating mechanism contained in said insulating housing and including a manually operable handle, a releasable member releasable to cause automatic opening of said relatively movable contacts, current responsive means for causing release of said releasable member upon the occurrence of predetermined current conditions through said contacts comprising a common trip bar extending across all of said pole chambers, a restraining latch normally engaging and restraining said releasable member, means connecting said common trip bar and said restraining latch to cause releasing movement of said restraining latch upon predetermined movement of said common trip bar, a current responsive device connected in circuit with each of said pairs of relatively movable contacts respectively, means connecting each of said current responsive means to said common trip bar, means for adjusting the current level at which each of said current responsive devices operates to cause releasing movement of said trip bar comprising a cam follower member pivotally supported in said insulating housing, means operated by said cam follower member for modifying the current sensitivity of at least one of said current responsive devices, a rotatable cam member engaging said cam surface of said cam follower member, said cam member being supported upon an elongated supporting shaft having at least a portion thereof threaded, a member in threaded engagement with said threaded portion of said supporting shaft and normally movable with said cam member upon rotation of said cam member, means for selectively restraining rotational movement of one of said supporting shaft and said normally movable member, whereby rotation of the other of said members causes relative movement between said shaft and said normally movable member in a direction parallel to the axis of rotation of said supporting shaft to thereby shift the position of said cam member relative to said main insulating housing in a direction parallel to the axis of rotation of said shaft and to cause said cam member to engage said cam surface at points of differing distances the pivotal support of said cam follower memher, said axis of rotation of said supporting shaft extending substantially parallel to said cam surface in at least one possible adjusted position of said cam follower member, and means accessible from outside of said main housing rotating said cam member.

11. A multi-pole electric circuit breaker comprising a main insulating housing having at least two pole chambers, at least one pair of movable contacts in each of said pole chambers, operating mechanism contained in said insulating housing and including a manually operating handle, a releasable member releasable to cause automatic opening of said relatively movable contacts, current responsive means for causing release of said releas able member upon the occurrence of predetermined current conditions through said contacts comprising a common trip bar extending across all of said pole chambers, a restraining latch normally engaging and restraining said releasable member, means connecting said common trip bar and said restraining latch to cause releasing movement of said restraining latch upon predetermined move ment of said common trip bar, a current responsive device connected in circuit with each of said pairs of relatively movable contacts respectively, means connecting each of said current responsive means to said common trip bar, means for adjusting the current level at which each of said current responsive devices operates to cause releasing movement of said trip bar comprising a cam follower member pivotally supported in said insulating housing, means operated by said cam follower member for modifying the current sensitivity of at least one of said current responsive devices, a rotatable cam member engaging said cam surface of said cam follower member, an elongated supporting shaft rigidly attached to said cam member, an adjusting nut in threaded engagement with of said supporting shaft to thereby shift the position of said cam member relative to said main insulating housing in a direction parallel to the axis of rotation of said shaft and to cause said cam member to engage said cam surface at points of differing distances from the pivotal support of said cam follower member selectively, said axis of said supporting shaft extending substantially parallel to said cam surface in at least one possible adjusted position of said cam follower member, and the means accessible from outside of said main insulating housing for rotating said cam member.

12. An electric circuit breaker trip unit comprising an insulaitng housing, an electrical conductor in said insulating housing having terminal portions accessible externally of said housing, a magnetic field piece supported in said insulating housing and arranged to be energized by current through said conductor, an armature supported in said insulating housing for movement toward and away from said magnetic field piece, spring means biasing said armature away from said field piece, means accessible externally of said insulating housing for adjusting the tension of said armature biasing spring, a cam follower member pivotally supported in said insulating housing and connected to said armature member for limiting the movement of said armature member away from said field piece in accordance with the position of said cam follower member, a cam member rotatably supported in said housing, means for permitting rotation of said cam member from outside of said housing, and means accessible externally of said housing for adjustably positioning said cam member to act on said cam follower member at points of differing distances from the pivotal support of said cam follower member selectively.

13. A trip unit for an electric circuit breaker comprising an insulating housing, an electrical conductor supported in said insulating housing and having terminal portions accessible externally of said housing, a magnetic field piece supported in said insulating housing and arranged to be energized by current through said conductor, an armature supported in said insulating housing for movement toward and away from said field piece, a biasing spring acting on said armature and biasing said armature for movement away from said magnetic field piece, a cam follower member pivotally supported in said insulating housing and having an elongated cam follower surface, means connected to said cam follower member to said armature to limit the movement of said armature away from said magnetic field piece in accordance with the position of said cam follower member, a cam member rotatably supported in said insulating housing, means accessible externally of said insulating housing for rotating said cam member, and means accessible externally of said housing for bodily moving said cam member to act on said cam follower member at points of differing distances from said pivotal support of said cam follower member selectively, said cam member being bodily movable along a path of movement extending substantially parallel to said cam follower surface in at least one possible adjusted position of said cam follower member.

14. An electric circuit breaker trip unit comprising an insulating housing, an electrical conductor in said insulating housing having terminal portions accessible externally of said housing, a magnetic field piece supported in said housing and arranged to be energized by current through said conductor, a movable armature movably supported in said housing for movement toward and away from said field piece, spring means biasing said armature away from said field piece, a cam follower member pivotally supported in said insulating housing and having an elongated cam follower surface, a rotatable cam member supported in said housing and engaging said cam follower member, an elongated supporting shaft supporting said cam member, an insulating knob on one end of said supporting shaft including a portion accessible from outside of said insulating housing, means for restraining rotational movement of said cam member, said supporting shaft including a threaded portion disposed and arranged to cause axial movement of said cam member along the axis of rotation of said shaft upon turning of said knob portion while said cammember is restrained from movement, whereby to cause said cam member to engage said cam follower portion at points of differing distance from the pivotal support of said cam follower member selectively.

15. An electric circuit breaker trip unit comprising a conductor, a magnetic field piece arranged to be energized by current through said conductor, an armature supported for movement toward and away from said field piece, spring means biasing said armature for movement away from said field piece, a pivotally supported stop member connected to said armature member to limit movement of said armature member away from said field piece in accordance with the position of said stop member, said stop member having a cam follower surface, a supporting shaft, a rotatable cam member supported on said supporting shaft, a knob threadedly engaged with said supporting shaft adjacent one end thereof, means supporting said knob for rotation in a plane fixed relative to said pivot of said stop member, and means for restraining rotation of said cam member whereby continued rotation of said knob member causes said supportshaft to thread axially through said tknob member and to move said cam member axially in the direction of said supporting shaft to adjustably position said cam memher to engage said cam follower surface at points of differing distance from said pivotal support selectively.

16-. An electric circuit breaker trip unit as set forth in claim 15 wherein said trip unit also comprises means accessible externally of said trip unit housing for adjusting the tension of said armature biasing spring.

17. An electric circuit breaker trip unit comprising an insulating housing, a conductor supported in said housing and having a terminal portion accessible externally of said housing, a magnetic field piece supported in said insulating housing and arranged to be energized by current through said conductor, an armature supported in said insulating housing for movement toward and away from said field piece, spring means biasing said movable armature for movement away from said field piece, means for limiting the movement of said armature away from said magnetic field piece comprising a cam follower member pivotally supported in said insulating housing, said cam follower member having an elongated cam follower surface, a rotatable cam member, an elongated shaft supporting said rotatable cam member and having a threaded portion adjacent to one end thereof, said cam member being fixedly supported on said supporting shaft, an insulating knob threadedly engaged with said threaded portion of said supporting shaft, said insulating knob being journalled for rotation in said insulating housing and including a portion extending externally of said insulating housing, said insulating knob also including an opening thereof in providing access to one end portion of said supporting shaft whereby said supporting shaft may be restrained from rotation by restraining means external of said insulating housing while said insulating knob is rotated to move said supporting shaft axially with respect to said insulating knob to thereby move said cam; member along said cam follower surface to engage said cam follower surface at points of differing distance from the pivotal support of said cam follower member, selectively.

18. An electric circuit breaker trip unit as set forth in claim 17 wherein said trip unit also includes means for closing said access aperture in said insulating 'knob.

19. An electric circuit breaker trip unit comprising an insulating housing, an electrical conductor supported in said insulating housing and including terminals accessible externally of said housing, a magnetic field piece supported in said insulating housing and arranged to be energized by current through said conductor, an armature assembly pivotally supported in said insulating housing and including a cam follower portion, an armature portion movable toward and away from said magnetic field piece and a latch actuating portion, spring means biasing said armature assembly for rotation about its pivotal support in a direction to move said armature portion away from said magnetic field piece, means accessible externally of said insulating housing for adjusting said spring means, a latch member pivotally supported in said insulating housing, a cam assembly comprising a cam member and an elongated supporting shaft carrying said cam member, said supporting shaft being rotatably supported at one end in said insulating housing, the other end of said supporting shaft being threadedly engaged in an insulating knob rotatably supported in said insulating housing, said insulating knob including an access opening providing access to one end of said supporting shaft externally of said insulating housing, said end of said supporting shaft including a nonsymrnetrical formation oriented in predetermined relation with said cam member, a closure cap for closing said access opening of said insulating knob, said closure cap also including a means cooperating with a portion of said insulating housing for limiting rotation thereof when mounted on said insulating 'knob, said cam follower surface extending substantially parallel to the axis of said supporting shaft in at least one position of said cam member.

References Cited in the file of this patent UNITED STATES PATENTS 2,268,340 Loomis Dec. 30, 1941 2,491,959 Dyer Dec. 20, 1949 2,586,326 Grissinger et al. Feb. 19, 1952 2,673,264 Cole Mar. 23, 1954 2,842,635 Cole July 8, 1958 2,884,497 Steven et a1. Apr. 28, 1959 

1. AN ELECTRIC CONTROL DEVICE INCLUDING A MEMBER MOVABLE TO VARY THE SENSITIVITY OF SAID DEVICE, MEANS FOR ADJUSTABLY POSITIONING SAID MOVABLE MEMBER COMPRISING A PIVOTED MEMBER HAVING A CAM FOLLOWER PORTION, A CAM MEMBER ACTING ON SAID CAM FOLLOWER PORTION, AND MEANS FOR BODILY MOVING SAID CAM MEMBER TO A PLURALITY OF DIFFERENT POSITIONS TO ACT ON SAID CAM FOLLOWER PORTION AT CORRESPONDING DIFFERING DISTANCES FROM THE PIVOTAL SUPPORT OF SAID PIVOTED MEMBER SELECTIVELY, SAID CAM MEMBER BEING ROTATABLE ABOUT A PREDETERMINED AXIS OF ROTATION WHEN IN EACH OF SAID POSITIONS TO MOVE SAID CAM FOLLOWER PORTION IN A DIRECTION SUBSTANTIALLY PERPENDICULAR TO SAID AXIS OF ROTATION. 